Bad news for the teachers’ unions: Viola Davis and Maggie Gyllenhaal in a scene from “Won’t Back Down,” the pro-school-reform drama.AP

Union protesters demonstrated outside the premiere of the new pro-education reform movie “Won’t Back Down.”

As well they should have. Just as tobacco executives should have protested at the opening of “The Insider.” And corporate polluters should have chanted taunts outside every theater showing “Erin Brockovich.” And CEOs of nuclear-power companies should have formed a human chain to block the red carpet at the premiere of “The China Syndrome.”

“‘Won’t Back Down,’ get out of town,” and “Move on over, corporate takeover,” the protesters at the “Won’t Back Down” premiere intoned. If their slogans were juvenile and the instincts thuggish, the calculation of their self-interest was exactly right — unions shouldn’t want anyone to see this film.

In an outraged public letter, the head of the American Federation of Teachers, Randi Weingarten, complained that the movie traffics in “the most blatant stereotypes and caricatures I have ever seen.”

Really? Weingarten must never have seen a World War II movie, or a film featuring a hooker with a heart of gold, or pretty much any romantic comedy.

What makes “Won’t Back Down” so objectionable to her isn’t that its characters are stereotypes but that they are revelations. Time-serving teachers beholden to a union obsessed with its prerogatives and power don’t often show up on the big screen, or we’d hear about more union pickets of movie openings.

“Won’t Back Down” is about a plucky working-class mother, played by Maggie Gyllenhaal, whose dyslexic daughter is “getting crushed,” as she puts it, at the awful local elementary school. She enlists a teacher at the school, played by Viola Davis, to work with her to trigger a parent-teacher takeover of the failing school.

A great contest between the reforming duo and the powers that be ensues, and — I’m probably not spoiling it for anyone if I reveal this — the duo prevails.

Critics point out how the story is overly simplistic and tugs too much on the heartstrings. But this is to be expected. It’s a morality tale, like so many other Hollywood movies with a point. The legend on the poster for “Erin Brockovich” reads: “She brought a small town to its feet and a huge company to its knees.” Did anyone go to it expecting fine-grained nuance?

The villain in “Won’t Back Down” is the system, with the union playing an outsize role in it. That makes it a more complex portrayal of education than the typical classroom movie that celebrates the heroic efforts of one teacher.

The teachers in “Won’t Back Down” are burdened by a lackluster principal, a deadening culture of mediocrity at their school and their fear of losing their union protections when presented with the possibility of something new.

If all she cares about is the depiction of the teachers in the movie, Weingarten should be pleased. Many of them — after agonizing over their loyalty to the union and considerations of their own interest — decide to do the right thing and support a radical reform of their atrocious school.

The chief producer of the film, Walden Media, has an interest in promoting educational change. It’s a sign of how deep the roots of education reform have sunk into the culture, though, that Maggie Gyllenhaal and Viola Davis appear in the film and broadly support its message.

Gyllenhaal stipulates that she’s pro-union, but all is not well with the teachers unions. Davis said of the protesters, “There was not one person — I guarantee you — that was outside there protesting with a picket sign who had their child in a failing school.”

In one scene in “Won’t Back Down,” a union official with a history of union organizing in her family asks plaintively, When did Norma Rae become the bad guy? When she became a cog in a union machine that protects an educational system that everyone knows isn’t working.

“Won’t Back Down” may make Randi Weingarten angry, but it mostly should make her afraid for her cause.